Last week I wrote about the difficulties encountered by conservation
biologists in establishing how many kinds of animals are present in
the world. The beach mice of Alabama and Florida served as an example
of an identifiable species of animal with variable habitat requirements
and coat colors. Hence, the issue could become clouded as to how many
kinds of animals, one or several, are actually represented. But even
if taxonomists did accomplish the impossible task of naming and agreeing
on all the species and subspecies of organisms, ecologists would be
confronted with another problem. How can the number of different kinds
of animals that live within a prescribed region be determined when individuals
of the species are difficult to find?

Some sort of field sampling effort is necessary to characterize biodiversity
of a prescribed area and is one of the first steps in conservation at
the ecosystem level. For instance, knowing the species of plants and
animals being protected by the country's extensive network of national
parks and wildlife refuges can make us more respectful of our natural
heritage. But to find out what we have, experts must do the counting,
and for some groups of animals, the task can be more challenging than
is at first apparent.

An
unsettled question that remains for many major groups of animals is
how closely the number of species that have been discovered and described
in a group represent the actual number present. The issue can be particularly
vexing for malacologists, scientists who study clams, mussels, and other
mollusks. Mollusks have the highest known species diversity of any animal
group native to the world's oceans. Mollusk biodiversity is especially
high in the tropical Indo?Pacific region, but some malacologists think
it is much higher than what has been described. For example, some estimates
are that the number of coral reef species currently described represent
as low as 1% of the species actually present. A recent study has put
to the test the idea that what has already been described woefully underrepresents
the actual numbers of mollusk species.

Philippe
Bouchet of the Museum National d'Histoire Naturelle, France, and colleagues
conducted an intensive survey of mollusk species at a site on the west
coast of New Caledonia in the Coral Sea east of Australia. The investigators
intensively sampled more than 100 square miles of coral reef lagoons,
collecting every mollusk shell that could be found. The scientific sampling
effort, more than 400 person?days was the most thorough ever made in
determining species diversity of mollusks. Aside from ending up with
the largest and most variable seashell collection ever made from one
place, the scientists also uncovered the truth about how well sampling
reflects reality for marine mollusks.

They
collected more than 127,000 individual mollusks of 2,738 species, numbers
that exceed any previous surveys of mollusks taken anywhere in the world
for a comparable area of coral reef. Rare species, defined as ones that
were represented by only a single specimen each, made up 20% of the
sample. This is important to note, because when one?fifth of the species
in a sample are represented by only one specimen, the likelihood increases
that lots of other rare species were present but never found. When the
investigators used a mathematical formula to estimate species numbers
beyond their actual captures, they calculated that as many as 3,971
species were actually present in the region sampled. Thus, biodiversity
was dramatically higher than ever before reported, confirming the suspicion
that the number of species of mollusks present around that part of New
Caledonia was much higher than could be determined by even the most
intensive sampling.

The
results from the New Caledonia study suggest that current estimates
of global biodiversity of mollusks are greatly underestimated. The same
is probably true of other groups of animals in many different regions
of the world on land, in freshwater, and in the sea. Among the important
lessons to be learned from that conclusion, consider this one: when
we demolish natural habitats, we are destroying even more species than
we realize.